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· The strongest two-category combinations were commuter tax benefits teamed with facilities
and amenities (6.8 percent VTR) and commuter tax benefits teamed with CWW (7.0 percent).
The poorest results seem to come when on-site services are combined with rideshare matching
(-3.2 percent VTR), non-financial incentives are paired with rideshare matching (-1.5 percent),
and non-financial incentives are teamed with on-site services (-1.3 percent). Such seeming anom-
alies often occur using models when complex modal tradeoffs are occurring in the calculations.
In this particular test, however, a combination like rideshare matching with on-site services
might be expected to lead to a more favorable result, given that the starting conditions are favor-
able to ridesharing over transit.
· There are only eight cases in the 66 pairs pictured in Table 19-33 where the pairing actually
results in a positive, or at least somewhat synergistic effect, i.e., the combination of the two
strategies leads to a trip reduction impact that is larger than either strategy individually. These
pairings are: commuter tax benefits teamed with CWW (7.0 percent VTR versus 5.0 percent and
3.8 percent individually) or with facilities and amenities (6.8 percent VTR versus 5.0 percent
and 4.1 percent individually), CWW with facilities and amenities (5.7 percent versus 3.8 per-
cent and 4.1 percent individually), parking management with facilities and amenities (4.2 per-
cent VTR versus 3.0 percent and 4.1 percent individually) or with marketing (4.5 percent VTR
versus 3.0 percent and 3.5 percent individually) or with financial incentives (4.8 percent VTR
versus 3.0 percent and 4.1 percent individually), and financial incentives with facilities and
amenities (4.9 percent VTR versus 4.1 percent and 4.1 percent individually) or with marketing
(4.9 percent VTR versus 4.1 percent and 3.5 percent individually). In none of these scenarios is
the synergy sufficient that the estimated trip reduction effect in combination is greater than the
sum of the separately applied individual strategies.
The Worksite Trip Reduction Model would appear to be an excellent start toward a set of tools that
can help TDM planners make sense of the vast number of strategies available to them. In addition
to being easy to use, a very appealing aspect of this new tool is that it does not seem to generate
unrealistic estimates of trip reduction. The predicted reductions are generally on the order of 3 to
6 percent. Reduction estimates of this magnitude compare more realistically with the typical
employment site results seen within large area-wide programs than do the 15 percent to 30 per-
cent reductions seen in the 82-program sample. It should once again be stressed that the 82 exam-
ples include many exemplary programs, and that that group should not in any way be construed
as typical of what might be realized in a large area-wide regulatory program.14
Practitioners are urged to apply caution and common sense to any model projection, whether it be
the two models featured in this subsection, or the FHWA TDM Evaluation Model, or the U.S.
Environmental Protection Agency (EPA) COMMUTER Model introduced later in the "Additional
Resources" section. Empirical case studies such as those presented in this chapter, or contained in
a number of the recommended resources, always serve as a good way of cross-checking a TDM
program's potential impact.
International Experience
Outside the United States, interest in TDM has been particularly high in the Netherlands and in
the United Kingdom. A study prepared for the British Department for Transport (DfT), Smarter
14 During the timeframe of the Chapter 19 review and publication process, CUTR issued an update to the
Worksite Trip Reduction model, now renamed TRIMMSİ (Concas and Winters, 2009). See the "Additional
Resources" section for additional information.
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Choices--Changing the Way We Travel (Cairns et al., 2002), provides a summary of TDM experience
in those two venues. Key studies and findings from the experience reviewed are summarized in
the following section.
Making Travel Plans Work15
This analysis and report was originally prepared for the DfT in 2002 by Cairns, Davis, Newson,
and Swiderska of ESRC Transport Studies Unit UCL, and Adrian Davis Associates. It represented
the biggest study of British workplace travel plans to date and presents results based on an analy-
sis of best practice at 20 organizations employing over 69,000 employees. These cases represented
a range of public and private organizations, all of which were selected as examples of good (not
average) practice. Taken overall, the 20 organizations had reduced the number of cars driven to
work by 14 for every 100 staff, representing an average reduction of 18 percent in the proportion
of commute trips by car driver. On average, the organizations had doubled the proportion of staff
commuting by bus, train, cycling, and walking, and car sharing (carpooling) had also been reason-
ably successful.
A study of factors that made some travel plans more successful than others produced very few
generalizations that could be made. All travel plans had involved real changes to employee travel
options, so it was not possible to assess the effects of plans that focused on awareness-raising only.
The one factor that did emerge was parking. For the 13 travel plans that had addressed parking,
either by restricting supply, introducing charges, or providing incentive payments to those giving
up a parking space, the proportion of commute trips made as car driver was reduced by 24 per-
cent, compared to 10 percent for those plans that had not addressed parking (Cairns et al., 2002).
Effective TDM at Worksites in the Netherlands and the United States
This study, performed by Organisational Coaching and Schreffler in 1996, compared 20 paired case
studies from the Netherlands and the United States. The organizations examined included a large
hospital, a large manufacturer, a government organization or utility, a bank, an insurance or
telecommunications organization, a major university, an airport, a consultancy firm, and a smaller
employer with less than 250 employees. Again, examples chosen were all considered to be success
stories. Results showed remarkable similarity across the two sets of case studies, with the programs
in the United States revealing VTR rates in a range of 6 percent to 49 percent, with an average of
19 percent, while those in the Netherlands had reductions in vehicle kilometers of travel ranging
from 6 percent to 32 percent, averaging 20 percent (Cairns et al., 2002).
Netherlands Ministry of Transport Study
A 1998 Dutch study by Ligtermoet included a review of new results from 40 organizations in the
Netherlands plus other Dutch data. Analysis showed that plans with "basic" measures (such as
car-sharing schemes) achieved vehicle kilometer reductions of 6 to 8 percent, while those with
"luxury" measures (such as company buses) or "push" measures (such as parking management)
achieved reductions in the range of 15 to 20 percent. This led to the conclusion that plans combin-
ing both "carrots and sticks" are the most effective (Cairns et al., 2002).
15 A "travel plan" is the equivalent of what is known in the United States as a Transportation Management
Plan (TMP) (Enoch and Zhang, 2008). United Kingdom experience with travel plan employer participation
rates is included in the "Site- Versus System-Level Impacts" subsection which follows.
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